1. Field of the Invention
The present invention relates to a mobile communication system for supporting uplink data transmission. More particularly, the present invention relates to a method and apparatus for transmitting/receiving control information about the uplink transmission status of a User Equipment (UE), required for Node B scheduling of uplink data transmission.
2. Description of the Related Art
A 3rd generation mobile communication system using Wideband Code Division Multiple Access (WCDMA) based on the European Global System for Mobile communications (GSM) system, and Universal Mobile Telecommunication Service (UMTS) provides mobile subscribers or computer users with a uniform service of transmitting packet-based text, digitized voice, and video and multimedia data at or above 2Mbps regardless of their locations around the world. The concept of virtual access has allowed the UMTS system to access any end point within a network at any time. Virtual access refers to packet-switched access using a packet protocol similar to Internet Protocol (IP).
FIG. 1 illustrates the configuration of the UMTS Terrestrial Radio Access Network (UTRAN) in a conventional UMTS system.
Referring to FIG. 1, a UTRAN 12 includes Radio Network Controllers (RNCs) 16a and 16b and Node Bs 18a to 18d, and connects a UE 20 to a Core Network (CN) 10. A plurality of cells may underlie the Node Bs 18a to 18d. Each RNC 16a or 16b controls its underlying Node Bs and each Node B controls its underlying cells. An RNC, Node Bs and cells under the control of the RNC collectively form a Radio Network Subsystem (RNS) 14a or 14b. 
The RNCs 16a and 16b each allocate or manage radio resources to the Node Bs 18a to 18d under their control. The Node Bs 18a to 18d function to actually provide the radio resources. The radio resources are configured on a cell basis and the radio resources provided by the Node Bs 18a to 18d refer to radio resources of the cells that they manage. The UE establishes a radio channel using radio resources provided by a particular cell under a particular Node B for communications. According to the UE, a distinction between the Node Bs 18a to 18d and their controlled cells is meaningless and the UE 20 deals only with a physical layer configured on a cell basis. Therefore, the terms “Node B” and “cell” are interchangeably used herein.
A Uu interface is defined between a UE and an RNC. The hierarchical protocol architecture of the Uu interface is illustrated in detail in FIG. 2. This interface is divided into a control plane (C-plane) 30 for exchanging control signals between the UE and the RNC and a user plane (U-plane) 32 for transmitting actual data.
Referring to FIG. 2, a Radio Resource Control (RRC) layer 34, a Radio Link Control (RLC) layer 40, a Medium Access Control (MAC) layer 42, and a physical (PHY) layer 44 are defined on the C-plane 30. A Packet Data Control Protocol (PDCP) layer 36, a Broadcast/Multicast Control (BMC) layer 38, the RLC layer 40, the MAC layer 42, and the PHY layer 44 are defined on the U-plane 32. The PHY layer 44 resides in each cell and the MAC layer 42 through the RRC layer 34 are configured in each RNC. The UE has all layers.
The PHY layer 44 provides an information delivery service by a radio transfer technology, corresponding to Layer 1 (L1) in an Open System Interconnection (OSI) model. The PHY layer 44 is connected to the MAC layer 42 via transport channels. Data processing in the PHY layer 44 determines the mapping relationship between the transport channels and physical channels.
The MAC layer 42 is connected to the RLC layer 40 via logical channels. The MAC layer 42 delivers data received from the RLC layer 40 on the logical channels to the PHY layer 44 on appropriate transport channels, and delivers data received from the PHY layer 44 on the transport channels to the RLC layer 40 on appropriate logical channels. The MAC layer 42 inserts additional information or interprets inserted data in data received on the logical channels and controls random access. A U-plane-related section is called MAC-data (MAC-d) and a C-plane-related section is called MAC-control (MAC-c) in the MAC layer 42.
The RLC layer 40 controls the establishment and release of the logical channels. The RLC layer 40 operates in an Acknowledged Mode (AM), an Unacknowledged Mode (UM) or a Transparent Mode (TM) and provides different functionalities in those modes. Typically, the RLC layer 40 segments or concatenates Service Data Units (SDUs) received from an upper layer to an appropriate size, and corrects errors.
The PDCP layer 36 resides above the RLC layer 40 in the U-plane 32. The PDCP layer 36 is responsible for compression and decompression of the header of data carried in the form of an IP packet and data delivery with integrity in the case where a serving RNC is changed due to the UE's mobility.
The characteristics of the transport channels that connect the PHY layer 44 to the upper layers depend on Transport Format (TF) that defines a PHY layer process including convolutional channel encoding, interleaving, and service-specific rate matching.
Particularly, the UMTS system uses an Enhanced Uplink Dedicated Channel (E-DCH) with the aim to improve packet transmission performance on the uplink from UEs to a Node B. To support more stable high-speed data transmission, the E-DCH utilizes Hybrid Automatic Retransmission request (HARQ) and Node B-controlled scheduling.
FIG. 3 illustrates typical uplink packet data transmission on the E-DCH via radio links. Reference numeral 100 denotes a Node B that supports the E-DCH and reference numerals 101 to 104 denote UEs that transmit the E-DCH.
Referring to FIG. 3, the Node B 100 evaluates the channel statuses of the UEs 101 to 104 and schedules their uplink data transmissions based on the channel statuses. The scheduling is performed such that a noise rise measurement does not exceed a target noise rise in the Node B 100 in order to increase total system performance. Therefore, the Node B 100 allocates a low data rate to a remote UE 104 and a high data rate to a nearby UE 101.
FIG. 4 is a diagram illustrating a typical signal flow for message transmission on the E-DCH.
Referring to FIG. 4, a Node B and a UE establish an E-DCH in step 202. Step 202 involves message transmission on dedicated transport channels. The UE transmits scheduling information to the Node B in step 204. The scheduling information may contain uplink channel status information which is the transmit power and power margin of the UE, and the amount of buffered data to be transmitted to the Node B.
In step 206, the Node B monitors scheduling information from a plurality of UEs to schedule uplink data transmissions for the individual UEs. The Node B decides to approve an uplink packet transmission from the UE and transmits scheduling assignment information to the UE in step 208. The scheduling assignment information may include a granted rate and an allowed timing.
In step 210, the UE determines the TF of the E-DCH based on the scheduling assignment information. The UE then transmits uplink packet data on an Enhanced-Dedicated Physical Data Channel (E-DPDCH) to which the E-DCH is mapped in step 214. The UE simultaneously transmits TF information to the Node B on an Enhanced-Dedicated Physical Control Channel (E-DPCCH) associated with the E-DCH in step 212. The Node B determines whether the TF information and the uplink packet data have errors in step 216. In the presence of errors in either of the TF information and the uplink packet data, the Node B transmits a Non-acknowledgement (NACK) signal on an ACK/NACK channel to the UE. When there are no errors in the TF information or the uplink packet data, the Node B transmits an ACK signal to the UE on the ACK/NACK channel in step 218.
In the latter case, the packet data transmission is completed and the UE transmits new packet data to the Node B on the E-DCH. Alternatively, the UE retransmits the same packet data to the Node B on the E-DCH.
As described above, the E-DCH is mapped to the E-DPDCH for channel encoding and modulation of transmission data. Control information about the E-DCH is transmitted simultaneously with transmission of the E-DCH on the E-DPCCH and the E-DPDCH. The E-DCH control information is scheduling information and TF information. The scheduling information represents the UE status, required for the Node B to schedule the uplink data transmission for the UE. The scheduling information is the UE's buffer status information and the uplink channel status information. Another piece of control information called a “Happy Bit” indicates the current UE's status. The TF information includes the data rate of the transmitted E-DCH data, HARQ operation information, and Quality of Service (QoS) information. The RF information is transmitted simultaneously with the E-DCH data.
The buffer status information and the uplink channel status information are transmitted together with the E-DCH data in a MAC-e Protocol Data Unit (PDU) on the E-DPDCH. Alternatively, the TF information and the “Happy Bit” are transmitted on the E-DPCCH associated with the E-DPDCH. The “Happy Bit” usually indicates whether the UE is satisfied with the allowed data rate set by scheduling, and it is always transmitted in the presence of E-DCH data. To improve the efficiency of uplink data transmission, a technique for differentially setting and interpreting the “Happy Bit” according to the transmission status of the UE is needed.
Accordingly, there is a need for an improved system and method to efficiently transmit control information about uplink packet data of a UE for use in uplink data transmission scheduling in a Node B.